Linear and nonlinear spectroscopic optical studies on free base porphyrins in different solvents

Abstract

Obtaining the linear and non-linear optical properties as well as the fluorescence lifetimes of organic or inorganic compounds by time-resolved or spectroscopic techniques is extremely important for the understanding of photophysical and photochemical processes, which may be applied in several areas. With the advent of short-time, intense pulse lasers, it became possible to study temporal resolutions and to better understand the evolution of chemical processes over time, such as breaking and / or formation of chemical bonds. In addition, excited states and their absorptions and temporal responses, not observed in measurements of linear spectroscopy, could be identified with the use of pulsed and high intensity lasers. Several chemical processes of fundamental importance have been observed as a function of time or the use of non-linear optical techniques, such as energy transfer; dynamics of hydrogen bonds; light-induced isomerizations and light-induced degradations, and at fast-time scales, etc. Therefore, this project will be focused on the linear optical characterization of two new porphyrins. These studies will be done in different solvents. Linear optical techniques such as stationary absorption and fluorescence will be used to determine the absorption and fluorescence regions of these porphyrins. Once these ranges have been identified, fluorescence quantum efficiency measurements and fluorescence anisotropy will be conducted to determine whether or not they are good light emitters for a particular spectral range. Fluorescence anisotropy will provide important information about possible electronic states. As a second part, the project will be directed to the time resolved fluorescence technique to determine the relaxation dynamics of the excited states and thereby quantify possible triplet states being formed upon excitation. This formation of the triplet states requires results obtained by linear optics, as well as results obtained by nonlinear optics. Nonlinear studies will be initiated after the candidate learns about the nonlinear optical techniques available in our laboratory, specific for the determination of triplet systems.